The present invention relates generally to methods for suppressing the influence of roll eccentricities on the control of the rolled product thickness in a roll stand, and more particularly to a method for suppressing the influence of roll eccentricities on the control of the rolled product thickness in a roll stand in which provision is made in the control of a dead zone which is insensitive to signal fluctuations caused by the roll eccentricities the zone width of the dead zone being varied as a function of the magnitude of the signal fluctuations.
In the control of the rolled product thickness in a roll stand, the difficulty exists that the rolled product thickness, as controlled variable of interest, cannot simply be measured in terms of control in an evaluable way at the location of its production, namely the roll gap, and can therefore not be used for directly controlling out disturbances such as, for example, eccentricities of the rolls. However, in accordance with the so-called gage meter principle, the instantaneous rolled product thickness h.sub.a in the region of the roll gap can be determined by computation from the setting position s of the rolls, the rolling force FW and the spring constant c.sub.G of the roll stand as ##EQU1## In the case of the so-called automatic gage control (AGC) method, proceeding from this relationship, the rolling force is detected by means of a rolling force detector and is used for controlling the rolled product thickness. If the roll gap is increased, for example because of an increase in the entry thickness of the rolled product, this leads to an increase in the rolling force FW; this increase is detected, and the setting position s of the rolls is reduced by the control, so that the rolling force FW is further increased and the rolled product thickness is controlled back again to its desired value. However, as equation (1) shows, the rolled product thickness h.sub.a is not available on its own, but only together with the roll eccentricity .DELTA.R, which causes a periodic increase and decrease of the rolling force FW in the rolling process. The increases and decreases, caused by the eccentricities, of the rolling force FW are, however, falsely interpreted by the AGC system as increase and decrease, respectively, of the roll gap, as a result of which the rolling force FW is automatically increased and decreased respectively, via the setting position s and the eccentricities are thus rolled into the rolled product to their full extent.
In order to prevent this negative influence of the roll eccentricities on the control of the rolled product thickness, it is known from DE-C 26 43 686 to provide in the control a dead zone, which is insensitive with respect to signal fluctuations caused by the roll eccentricities. In this arrangement, the width of the dead zone is varied as a function of the amplitudes of the signal fluctuations and is thus matched to the extent of the eccentricities. For recording the amplitudes of the signal fluctuations, limiting value detectors having staggered response values and flip-flops arranged downstream from the limiting value detectors are used, as a result of which limits are placed on the accuracy.
The present invention is therefore directed to the problem of developing a method for suppressing the influence of roll eccentricities on the control of the rolled product thickness in a roll stand in which a dead zone is provided in the control, and in which the match of the width of the dead zone as a function of the eccentricities occurring is optimized.